Add Homebrew bash 4+ link for update instructions
Merge pull request #14 from billyboozer/master

Add Homebrew bash link for update instructions
Fix documenation for Bash 4
Update todo list

I am about to start major development. The future should bring a version
of polka that is easier to uninstall and keep separated from the rest of
your system.
Merge remote-tracking branch 'bosshack/polka'